promise-stream

"What happens when an unblockable force meets an immutable object?" - Lyndon Maydwell

A promise stream serves the same purpose as a blocking lazy sequence. Javascript code may not block and so an asynchronous alternative is required.

Example

Using promise-streams we can avoid callback hell and create functional code that elegantly expresses our data flow, regardless of whether that data is gathered asyncronously.

(let [changes   (event-stream ($ :#query) "change")
      keyups    (event-stream ($ :#query) "keyup")
      events    (concat* changes keyups)
      queries   (mapd* (comp :value summarise) events)
      responses (map*  perform-search queries)
      groups    (mapd* group-names responses)]
  (mapd* set-query-title!  queries)
  (mapd* set-results-stream! groups))

Here we are merging two streams that represent all change and keyup events that will ever occur on the query input. Once merged we pull the value out of the raw event and use it to search for groups on flickr. The responses are transformed into streams of names which are then rendered on the page.

Project structure

Utility scripts can be found in the script directory. Here you can start the repl, or a watcher that will automatically build.

Roadmap

• Wrap pcells in some protocols and have everything hit them through those.
• Switch from jayq deferreds to google closure deferreds.
• Setup propper failure propogation.
• Look into making the sequences more lazy with some consumer producer coordination.

License

Copyright © 2013 Logan Campbell

Distributed under the Eclipse Public License, the same as Clojure.